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M. Sullivan Machine Advisory Committee Review December 13-15, 2004

IR NEG Heating and Upgrade. M. Sullivan Machine Advisory Committee Review December 13-15, 2004. Outline. History from last run Summer work Vacuum model Conclusions. The NEG story.

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M. Sullivan Machine Advisory Committee Review December 13-15, 2004

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  1. IR NEG Heating and Upgrade M. Sullivan Machine Advisory Committee Review December 13-15, 2004

  2. Outline • History from last run • Summer work • Vacuum model • Conclusions

  3. The NEG story • When we regenerated the NEGs in IR2 on March 24 we began to wonder if some of the NEGs were starting to heat up from HOM power. • MAC Review in April • We confirmed that some were getting hot shortly thereafter but we did not get a full picture until the next ROD on June 3 when we instrumented every NEG in the upstream LER beam line. Regeneration temperature is about 750 °F

  4. Upstream LER plan view Quad chambers Dipole chambers Collimators 130F bot 150F bot 136F side 160F side 150F bot 150F bot LER current 2.2 A 268F 724F 425F 453F

  5. Collimator 453F 724F Collimator 268F

  6. 350 °F LER NEG Pump Temperatures Lab test data of NEG outgassing as a function of temperature Upstream LER side

  7. Data from the two hottest NEGs 3149 Pump pressure of 3147. The ion pump is between the two NEGs NEG temperatures 3142 3149

  8. LER NEG Test chamber

  9. Test NEG data over the summer We held the test NEG at our regen temperature for a month with a Turbo pump attached

  10. Pressure in the test NEG After the first 6 hrs Pressure as a function of time in the test NEG. Holding the NEG at the regen temperature of 725 F (400 C). After about 48 hrs

  11. Some regeneration details NEG heaters off NEG heaters on St707 Ion pumps on 10-2 Ion pumps off 600° C 500° C 10-4 400° C Hydrogen Equilibrium Pressure (Torr) Embrittlement Limit (20 Torr l/g) 10-6 300° C 10-8 200° C 10-10 10-2 10-1 100 101 Hydrogen Concentration Torr l/g 100 • Heat NEGs for 1 hr • 400-450 degC • Time 11:45-12:45 • Tubro cart pump: 220 L/s • Pressure at pump about 10-5 Torr

  12. LER upstream NEG work • This summer: • We took out the nine NEGs with “c type” screens and installed a small HOM absorber in each cavity • The total length of NEG pumping that was removed is 5.5 m out of a total of 40.4 m • We removed the two movable collimators • We removed the Q4 NEG and have replaced it with a HOM absorber (another 1.6 m of pumping) • We have added extra pumping at the port between the upstream LER Q4 and Q5 chambers • In addition, we have added extra screening to the ion pumps in this region

  13. Existing 3082 chamber Quad extrusion BPM Cooling bar BPM NEG plenum Chamber support NEG heater

  14. SiC HOM absorber Chamber shown inverted and plenum not shown for clarity

  15. Part of one of the NEG pumps that was removed this last summer

  16. One of the collimators that was removed • The NEG in this chamber was one of the hottest

  17. HOM absorber to replace NEG pump

  18. Drawing of installed extra pumping

  19. Vacuum model • We have started building a vacuum model of straight 2 • Had great help getting started by a summer student (Edward Young) • We have a preliminary model of the LER upstream beam pipe • Still need to check on screen conductances and on outgassing values from SR fans • Nevertheless we can get some idea about what happens to the vacuum pressure profile with the above LER NEGs removed

  20. Chamber Model Layout 3 69.33 m HER downstream LER downstream 4 plot plot Q5 NEG ST plot 2 1 Support chamber Q5 NEG plot plot 5 6 LER upstream HER upstream 66.114 m

  21. Support tube Vacuum Design Model Vacuum pressure in the support tube. The model predicts a pressure peak at the IP of about 20 nTorr.

  22. No radial ion pumps We lost these pumps a couple of years ago. One developed an Argon instability before it died . Both pumps do not work right now. We intend to replace these pumps during the next downtime.

  23. Upstream LER Ideal LER beam line from Q2 septum to about 63 m upstream

  24. Upstream LER after summer down

  25. HER scrubbing

  26. HER Upstream Q5 chamber • We plan to replace this chamber NEG temp in Q5 chamber Diamond BW (HER) BaBar Deadtime

  27. The upstream HER NEGs and heater instrumentation The upstream HER beam pipe is also blanketed with NEG pumps starting at 21 m and going out to about 45 m from the IP There are a total of 4 vacuum chambers in this region with NEG pumping (6 long NEGs). All of the pumps are below the beam chamber. The screen is very similar if not identical to the “c type” screen seen in the LER The collimator at 35 m has a TSP The only chamber in this area without pumping is the fast kicker chamber

  28. HER upstream NEG screen This is a post at the center of the chamber

  29. NEG heater temperature through heater resistance • Stan Ecklund has installed a circuit that measures some of the heater rod resistances • He has instrumented: • LER upstream • Q4 + Q5 (same circuit) • BV1 + next outboard (3042) (same circuit) • HER • Q5 downstream • Q5 upstream • BLF upstream This particular NEG pump can not be instrumented any other way

  30. BV1 NEG Temperature plot of first “c” chamber in LER (BV1) using resistance measurement Temperature plot of first “c” chamber in LER (BV1) Agreement is no better than about 20%. The signal is complicated by the resistance being the sum of the leads plus another NEG heater

  31. Q5 NEGs Q5 downstream Q5 upstream The upstream Q5 NEG resistance matches the TC we have in that NEG Conclusion: Downstream HER Q5 NEG is hotter than the upstream HER Q5 NEG

  32. Upstream HER BLF NEG So far, this NEG looks OK We think we will be OK for run 5 We have instrumented all of these upstream NEGs with TCs This NEG is located 22-24.5 m from the IP

  33. Conclusions • We have fixed the NEG pumps in the upstream LER beam pipe that were getting the hottest by removing the pumps and installing a HOM absorber in the pump cavity • We removed the NEG pump that was closest to the septum chamber because HOM power was also heating up that pump and installed a HOM absorber in its place • We removed the two movable collimators • The run 5 beam parameters will increase the HOM power we have so far experienced by increasing the beam currents and shortening the bunches • HOM power in IR2 will go up • We have instrumented the upstream HER NEGs and we will be watching them very carefully during this coming run

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